Many industrial processes can be improved by continuous, precise and reliable measurement of gas humidity. In processes such as flue gas desulfurization (FGD), solid particles with cohesive or adhesive properties are present in the gas stream at temperatures approaching the adiabatic saturation temperature; in these cases, continuous measurement of gas humidity using systems of the prior art is problematic. Common problems include condensation, agglomeration, adhesion and accumulation of solids on the humidity sensor causing interference with signal continuity, precision and reliability. These problems may be compounded by the presence of aqueous chemical compounds, such as calcium chloride, that exist in liquid form at temperatures substantially above the adiabatic saturation temperature.
The FGD process is an example in which continuous, precise and reliable measurement of gas humidity can be advantageous. FGD systems are intended to remove pollutants including sulfur dioxide, hydrochloric acid and mercury produced during the combustion of organic matter such as coal, biomass or municipal waste. More specifically, gas humidity and related parameters (such as dew point temperature, wet bulb temperature and adiabatic saturation temperature) are well known to affect pollutant removal rate, reagent consumption and corrosion rate at specific locations within “dry”, “semi-dry” or “spray dryer” type FGD systems. At these locations, most notably at the exit of the absorber vessel upstream of the particulate removal device, continuous humidity sensing systems of the prior typically fail due to agglomeration of particulate matter and liquids (such as saturated aqueous solutions of calcium chloride) that may exist above the adiabatic saturation temperature of water.
Therefore, there is a need in the art for a humidity sensing system that is fully automatic, accurate, precise, reliable and cost effective to operate in particulate laden gas streams at temperatures approaching the adiabatic saturation temperature.